You can find those streams in Icecast plugin->Formats->WebM or Ogg Theora or NSV

ST can look at the Content-Type: video/webmContent-Type: video/webmbut interesting question is how is should be with OGG Theora as by RFC3534 Content-Type: application/ogg could be presented for both audio and video streams so it needs additional probing. But by RFC5334 it is set explicitly as video/ogg and audio/ogg correspondingly.

Interesting thing is - ST already plays WebM and NSV direct links if you pase them via WebUI. But fails if you supply m3u link via icecast route. So changes could be minor.